MsgBox after not finding a value - excel

Question

I have a macro that runs an InputBox in which user types number and then excel finds a cell in a certain range which contains that value. I'd like to make an MsgBox which would make an alert if given number is not found and run InputBox again until the value is in range.
I have kinda idea how do I do it, but can't make the finding itself work. I've recorded a macro but don't know how to set it properly if it doesn't find anything.
My code so far:
Sub leftbutton()
Start: n = InputBox("Podaj numer punktu z wykresu") 'give me a point number from a chart
If n = "" Then Exit Sub
If n = "0" Then
MsgBox ("Liczba musi byc wieksza od zera") 'number must be > 0
GoTo Start
End If
If Not IsNumeric(n) Then
MsgBox ("Podaj liczbe!") 'give me a number!
GoTo Start
End If
Range("AS3:AS50000").Select
if
Selection.Find(What:=n, After:=ActiveCell, LookIn:=xlFormulas, _
LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:=xlNext, MatchCase _
:=False, SearchFormat:=False).Activate 'now how to know if it finds value or not?
Then msgbox("Nie ma takiego punktu na wykresie") 'there's no such point on a chart
Goto Start
Else '~> select cell with the found value
End If
End Sub

Answer 1

Code below will check in your range you specified and either give you error if nothing is found or row number of cell with match.
Dim FindResult As Object
n=... 'set whatever value you want to find
Range("AS3:AS50000").Select
Set FindResult = Selection.Find(n, LookIn:=xlFormulas, LookAt:=xlWhole)
If FindResult Is Nothing Then
MsgBox ("missing")
Else
MsgBox (FindResult.Row)
End If